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How can I list highest version of a kernel in perl – CentOS

In many docker container, le /boot is empty. Though, the vmlinuz is available in /var/lib/modules/<kver>/vmlinuz

In shell, I can do:

for kver in $(ls /lib/modules|sort -Vr)
do
    test -f /lib/modules/$kver/vmlinuz && echo $kver && break
done

How can I do this un perl in a reliable way (I mean: using modules that are present in CentOS-6 to CentOS-8 or any other Linux distro.

I’ve seen that modules for kernel version comparison or version sorting, but none are available as distro package in all release of CentOS ranging from 6 to 8 included (8 is important as it s a clone of RHEL-8 and RHEL-8 is extremely stripped down distro regarding perl packages).

If I have those 2 versions: 4.18.0-144.el8.x86_64 4.18.0-80.7.1.el8_0.x86_64 I need to chose the -144 one.

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2

Answers


  1. 0

    The easiest way to do this would be to use the Sort::Versions module (which you’d need to install from CPAN).

    #!/usr/bin/perl

use strict;
use warnings;
use feature 'say';

use Sort::Versions;
use File::Basename;

for (sort { versioncmp($b, $a) } glob '/lib/modules/*') {
  my $ver = basename $_;
  if (-e "/lib/modules/$ver/vmlinuz") {
    say $ver;
    last;
  }
}

    Update: Your question includes this:

    I’ve seen that modules for kernel version comparison or version sorting, but none are available as distro package in all release of CentOS ranging from 6 to 8 included

    Of course, packages aren’t the only way to install CPAN modules. You could always use cpan or cpanm. But if you really don’t want to install a module that way, then you could also cut and paste the versioncmp() subroutine into your code. It’s only a few dozen lines of code.

    sub versioncmp ($$) {
    my @A = ($_[0] =~ /([-.]|d+|[^-.d]+)/g);
    my @B = ($_[1] =~ /([-.]|d+|[^-.d]+)/g);

    my ($A, $B);
    while (@A and @B) {
        $A = shift @A;
        $B = shift @B;
        if ($A eq '-' and $B eq '-') {
            next;
        } elsif ( $A eq '-' ) {
            return -1;
        } elsif ( $B eq '-') {
            return 1;
        } elsif ($A eq '.' and $B eq '.') {
            next;
        } elsif ( $A eq '.' ) {
            return -1;
        } elsif ( $B eq '.' ) {
            return 1;
        } elsif ($A =~ /^d+$/ and $B =~ /^d+$/) {
            if ($A =~ /^0/ || $B =~ /^0/) {
                return $A cmp $B if $A cmp $B;
            } else {
                return $A <=> $B if $A <=> $B;
            }
        } else {
            $A = uc $A;
            $B = uc $B;
            return $A cmp $B if $A cmp $B;
        }       
    }
    @A <=> @B;
}
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  2. 0

    Is it cheating to use ls within perl?

    for (`ls -rv /lib/modules/`){
  chomp;
  next unless -e "/lib/modules/$_/vmlinuz";
  say; 
  last;
}
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